As a material of a case 55 of a light emitting device 51 (an LED package) illustrated in FIG. 3A1, conventionally, polyphthalamide (PPA), liquid crystal polymers, or other materials have been mainly used. In order for the case 55 to function also as a reflector, white dyes were contained in the case such that the case is formed into white with high reflectivity. However, PPA deteriorates due to heat and light from an LED chip 52, the intrusion of oxygen, or other factors, and, as illustrated in FIG. 3A2 as a browned part 58 represented by horizontal hatching, the white turns brown, thereby decreasing the reflectivity and hence decreasing luminous intensity of the package, and causing the end of life of the light emitting device 51.
In order to solve this browning, there is described the use of high heat-resistant polymers such as polycyclohexylene dimethylene terephthalate (PCT) as the material of the case in Patent Literatures 1 to 3.
Organic components of the case 55, a sealant 56, a die bond material 54, or other materials deteriorate due to heat, light, the intrusion of oxygen, or other factors. This deterioration may cause peeling at the boundary surface between the case 55 and the sealant 56 to form a gap 59, as illustrated in FIG. 3A2, whereby the reflective performance may decrease. However, because the deteriorated components are released outside the package through the gap 59, the deteriorated components themselves were less problematic.